In various systems, e.g., automotive heating, ventilation and air condition (HVAC) systems, it is desirable to track the position of a motor or other actuator. For example, automotive HVAC systems have used a DC motor to position ventilation doors to mix hot and cold air to achieve a desired mixed air temperature and to direct the mixed air to a desired location within a motor vehicle. The generation of accurate motor or actuator position information is desirable to accurately maintain various controlled components, e.g., ventilation doors, at an appropriate position.
In general, automotive HVAC systems have tracked the location of each door with a pulse count system. Typical pulse count systems have included a microcontroller, which has included a number of internal counters that have each been indirectly coupled to an output of an actuator to receive pulses to indicate a door position. Depending upon the degree of rotation of a shaft of the motor, an associated internal counter of the microcontroller is modified an appropriate amount.
Unfortunately, pulse count systems that have used a microcontroller in this manner have experienced an increasing time demand on the microcontroller as the number of actuators in a particular pulse count system have grown. In newer automotive HVAC systems as many as twenty actuators may be utilized within the system, with each actuator providing pulse counts. As more actuators have been utilized in a given HVAC system, it has been proposed that pulse count systems migrate to higher-end microcontrollers, e.g., from an 8-bit microcontroller to a 16-bit microcontroller. Unfortunately, migration to higher-end microcontrollers, if implemented, adds significant additional material cost to the automotive HVAC system.
In a typical automotive pulse count system, pulses may be provided as rapidly as one per millisecond, which has generally required the microcontroller to poll its input lines as often as every five hundred microseconds or use an interrupt to detect the pulses provided to the microcontroller from the various actuators. One solution is to operate the microcontroller of the HVAC system at a higher clock frequency to reduce the actuator associated time demands on the microcontroller. However, in automotive applications the clock frequency of a given microcontroller is normally limited due to electromagnet interference (EMI) considerations. Thus, as the number of actuator outputs continues to grow, the internal counter requirements for a microcontroller of an automotive HVAC system have accordingly increased.
Thus, what is needed is a pulse count system that is practical, economical and capable of handling an increasing number of actuators, as is typical in newer automotive HVAC systems, while operating at frequencies that do not greatly increase EMI considerations.